Chen Weijie

The formation of Pb–S bonds between perovskite and 2-mercapto-1-methylimidazole appreciably reduces surface trap and improves interfacial energy level alignment. The open circuit voltage of inverted inorganic perovskite solar cells is enhanced by 120 mV, yielding a power conversion efficiency of 20.6%, along with improved ambient stability.

Abstract

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n–i–p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI_{3− x} Br _x films with 2-mercapto-1-methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb²⁺ from perovskite by forming Pb–S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron-transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open-circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm² area and 17.3% for 1 cm² area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs.

Herein, an interpretable machine learning model for efficiency prediction of ternary organic solar cells based on nonfullerene acceptor is developed. It is based on effective molecular descriptors only. Remarkably, the high accuracy (coefficient of determination (R ²) > 0.9) can be achieved by constructing the machine learning model with a fewer number of descriptors.

The challenge of accurately predicting the power conversion efficiency (PCE) of ternary organic solar cells (OSCs) based on a nonfullerene acceptor holds the key to the rational design of a ternary blend. Developing an effective descriptor with experimentally measurable and theoretically computable signatures for accurately predicting the PCE of OSCs based on nonfullerene acceptors is an important step toward achieving this goal. Herein, the electronegativity is first proposed as an effective molecular descriptor for predicting the PCE of OSCs based on nonfullerene acceptors and further analyzing the underlying relationships between material property and device performance. Remarkably, the high accuracy (Coefficient of Determination) > 0.9) can be achieved by constructing the machine learning model with a fewer number of descriptors. In addition, the SHapley Additive exPlanations approach is introduced to provide both local and global interpretations for extracting a deep understanding of complex molecular descriptor–PCE relationships. These results in this study validate the effectiveness of the molecular descriptor, providing an efficient modality for rapid and precise screening of high-performance ternary materials.

1,2-diiodotetrafluorobenzene (1,2-DITFB) is selected to form the bidentate coordination bonding with undercoordinated iodide ion of the perovskite surface. The stable perovskite/1,2-DITFB heterostructure can effectively suppress iodide ion migration into the functional layer and inhibit the release of I₂. The unencapsulated champion device maintains 96% of its initial value after aging under operational conditions for 500 h.

It has been reported that one of the influencing factors leading to stability issues in iodine-containing perovskite solar cells is the iodine loss from the perovskite layer. Herein, bidentate coordination is used with undercoordinated I⁻ of the perovskite surface to construct the stable perovskite-based heterostructure. This strong halogen bonding effectively inhibits interfacial migration of I⁻ into functional layers such as C₆₀ and Ag. Moreover, passivation of the undercoordinated I⁻ suppresses the release of I₂ and further delays the formation of voids at the perovskite surface. The resulting inverted perovskite solar cell exhibits a power conversion efficiency of 22.59% and the unencapsulated device maintains 96.15% of its initial value after continuous operation for 500 h under illumination.

Small amount of amphoteric l-Asparagine additive in tin perovskites effectively passivates the cationic and anionic charged defects and regulates the nucleation/crystallization process in the film as well as prevents the tin oxidation, resulting in improved morphology of the tin perovskite film with a remarkable efficiency of 13.31% and superior operational stability.

Abstract

Despite the optoelectronic similarities between tin and lead halide perovskites, the performance of tin-based perovskite solar cells remains far behind, with the highest reported efficiency to date being ≈14%. This is highly correlated to the instability of tin halide perovskite, as well as the rapid crystallization behavior in perovskite film formation. In this work, l-Asparagine as a zwitterion plays a dual role in controlling the nucleation/crystallization process and improving the morphology of perovskite film. Furthermore, tin perovskites with l-Asparagine show more favorable energy-level matching, enhancing the charge extraction and minimizing the charge recombination, leading to an enhanced power conversion efficiency of 13.31% (from 10.54% without l-Asparagine) with remarkable stability. These results are also in good agreement with the density functional theory calculations. This work not only provides a facile and efficient approach to controlling the crystallization and morphology of perovskite film but also offers guidelines for further improved performance of tin-based perovskite electronic devices.

Uncompleted solvent-assisted complexation effects are found to cause disordered crystallization and phase segregation in mixed halide perovskite film. By introducing the zwitterionic molecule aminoethanesulfonic acid into the precursor, a uniform film with much-improved phase stability can be realized. A new performance record of 19.66% is obtained for wide-bandgap (1.77 eV) p-i-n devices.

Abstract

Disordered crystallization and poor phase stability of mixed halide perovskite films are still the main factors that compromise the performance of inverted wide bandgap (WBG; 1.77 eV) perovskite solar cells (PSCs). Great difficulties are evidenced due to the very different crystallization rates between I- and Br-based perovskite components through DMSO-alone assisted anti-solvent process. Here, a zwitterionic additive strategy is reported for finely regulating the crystal growth of Cs_0.2FA_0.8Pb(I_0.6Br_0.4)₃, thereby obtaining high-performance PSCs. The aminoethanesulfonic acid (AESA) is introduced to form hydrogen bonds and strong PbO bonds with perovskite precursors, realizing the complete coordination with both the organic (FAI) and inorganic (CsI, PbI₂, PbBr₂) components, balancing their complexation effects, and realizing AESA-guided fast nucleation and retarded crystallization processes. This treatment substantially promotes homogeneous crystal growth of I- and Br-based perovskite components. Besides, this uniformly distributed AESA passivates the defects and inhibits the photo-induced halide segregation effectively. This strategy generates a record efficiency of 19.66%, with a V _oc of 1.25 V and FF of 83.7% for an MA-free WBG p-i-n device at 1.77 eV. The unencapsulated devices display impressive humidity stability at 30 ± 5% RH for 1000 h and much improved continuous operation stability at MPP for 300 h.

The industrialization of perovskite solar cells requires selecting adequate materials and processes to make them economically viable and environmentally sustainable. Nanocrystalline nickel oxide produced through flash infrared annealing reduces the time, cost, energy, and the amount of solvents required to produce hole transport layers in perovskite solar cells while increasing device performance and stability.

Abstract

The industrialization of perovskite solar cells requires adequate materials and processes to make them economically viable and environmentally sustainable. Despite promising results in terms of power conversion efficiency and operational stability, several hole-transport layers currently in use still need to prove their industrial feasibility. This work demonstrates the use of nanocrystalline nickel oxide produced through flash infrared annealing (FIRA), considerably reducing the materials cost, production time, energy, and the amount of solvents required for the hole transport layer. X-ray photoelectron spectroscopy reveals a better conversion to nickel oxide and a higher oxygen-to-nickel ratio for the FIRA films as compared to control annealing methods, resulting in higher device efficiency and operational stability. Planar inverted solar cells produced with triple cation perovskite absorber result in 16.7% power conversion efficiency for 1 cm² devices, and 15.9% averaged over an area of 17 cm².

In blends with polymerized small-molecule acceptors (PSMAs), the π–π molecular stacking is reduced, which decreases the conversion from local excitations to intra-moiety delocalized excitations in PSMAs and leads to radiative loss from local excitations during charge generation. Moreover, triplet losses of charge recombination are suppressed because of the reduced donor: acceptor interfaces in PSMA based blends.

Abstract

Polymerizing small-molecular acceptors (SMAs) is a promising route to construct high performance polymer acceptors of all-polymer solar cells (all-PSCs). After SMA polymerization, the microstructure of molecular packing is largely modified, which is essential in regulating the excited-state dynamics during the photon-to-current conversion. Nevertheless, the relationship between the molecular packing and excited-state dynamics in polymerized SMAs (PSMAs) remains poorly understood. Herein, the excited-state dynamics and molecular packing are investigated in the corresponding PSMA and SMA utilizing a combination of experimental and theoretical methods. This study finds that the charge separation from intra-moiety delocalized states (i-DEs) is much faster in blends with PSMAs, but the loosed π–π molecular packing suppresses the excitation conversion from the local excitation (LE) to the i-DE, leading to additional radiative losses from LEs. Moreover, the increased aggregations of PSMA in the blends decrease donor: acceptor interfaces, which reduces triplet losses from the bimolecular charge recombination. These findings suggest that excited-state dynamics may be manipulated by the molecular packing in blends with PSMAs to further optimize the performance of all-PSCs.

Electrochemical impedance measurements on blends of PM6:Y6 allow to derive a binding energy of 150 meV for the CT state, even though exciton dissociation is known to be barrierless. This study illustrates how aggregation of Y6 can account for this phenomenon.

Abstract

In an endeavor to understand why the dissociation of charge-transfer (CT) states in a PM6:Y6 solar-cell is not a thermally activated process, measurements of energy-resolved impedance as well as of intrinsic photoconduction are employed. This study determines the density of states distributions of the pertinent HOMO and LUMO states and obtains a Coulomb binding energy (E _{b , CT}) of ≈150 meV. This is 250 meV lower than the value expected for a pair of localized charges with 1 nm separation. The reason is that the hole is delocalized in the polymer and the electron is shared among Y6 molecules forming a J-like aggregate. There are two key reasons why this binding energy of the CT state is not reflected in the temperature dependence of the photocurrent of PM6:Y6-diode: i) The e–h dissociation in a disordered system is a multi-step process whose activation energy is principally different from the binding energy of the CT state and can be substantially less than E _{b , CT}, and ii) since dissociation of the CT state competes with its intrinsic decay, the dissociation yield saturates once the rate of dissociation grossly exceeds the rate of intrinsic decay. This study argues that these conditions are met in a PM6:Y6-solar cell.

Within this review, the recent advances on the application of wide band-gap insulating materials in perovskite solar cells, their types and preparation methods, as well as the related working mechanisms and existing problems are reviewed, with the aim of promoting the commercialization of perovskite solar cells.

Abstract

In recent years, the development of perovskite solar cells (PSCs) is advancing rapidly with their recorded photoelectric conversion efficiency reaching 25.8%. However, for the commercialization of PSCs, it is also necessary to solve their stability issue. In order to improve the device performance, various additives and interface modification strategies have been proposed. While, in many cases, they can guarantee a significant increase in efficiency, but not ensure improved stability. Therefore, materials that improve the device efficiency and stability simultaneously are urgently needed. Some wide band-gap insulating materials with stable physical and chemical properties are promising alternative materials. In this review, the application of wide band-gap insulating materials in PSCs, including their preparation methods, working roles, and mechanisms are described, which will promote the commercial application of PSCs.

Herein, a solution-mediated ligand exchange (SMLE) strategy is reported for the first time as a general approach to exchange the ligand and passivate vacancy of FAPbI₃ perovskite quantum dot (QD), which is exploited for improved carrier transport and reduced trap density, leading to a record high efficiency of 15.10% for all reported FAPbI₃ perovskite QD solar cell.

Abstract

Organic–inorganic formamidinium lead triiodide (FAPbI₃) hybrid perovskite quantum dot (QD) is of great interest to photovoltaic (PV) community due to its narrow band gap, higher ambient stability, and long carrier lifetime. However, the surface ligand management of FAPbI₃ QD is still a key hurdle that impedes the design of high-efficiency solar cells. Herein, this study first develops a solution-mediated ligand exchange (SMLE) for preparing FAPbI₃ QD film with enhanced electronic coupling. By dissolving optimal methylammonium iodide (MAI) into antisolvent to treat the FAPbI₃ QD solution, the SMLE can not only effectively replace the long-chain ligands, but also passivate the A- and X-site vacancies. By combining experimental and theoretical results, this study demonstrates that the SMLE engineered FAPbI₃ QD exhibits lower defect density, which is beneficial for fabricating high-quality QD arrays with desired morphology and carrier transport. Consequently, the SMLE FAPbI₃ QD based solar cell outputs a champion efficiency of 15.10% together with improved long-term ambient storage stability, which is currently the highest reported value for hybrid perovskite QD solar cells. These results would provide new design principle of hybrid perovskite QDs toward high-performance optoelectronic application.

A ternary blend strategy with one donor (D18) and two acceptors (BTP-eC9-4F and SM16) is put forward to fabricate organic solar cells (OSCs) with green-solvents. The addition of SM16 as the third component can induce better bicontinuous interpenetrating networks, reduce the energy losses in OSCs. Finally, the ternary devices can afford a much higher efficiency of 18.20% than the binary ones.

Abstract

Nowadays, it is still a great challenge to obtain high-performance green-solvent-processed organic solar cells (OSCs). In this study, a ternary blend strategy (one donor and two acceptors, 1D/2A) is developed to solve the difficulty of film morphology modulation during the fabrication of high-performance green-solvent-processed OSCs. A typical high-performance halogenated-solvent processable binary system D18:BTP-eC9-4F is selected as the host, its green-solvents-processed devices show an inferior power conversion efficiency (PCE) of ≈16%. SM16 with two 3D shape persistent end groups is selected as the third component due to its high fluorescence quantum yield, reduced intermolecular interaction, good solubility, and moderate crystallinity. As a result, the ternary devices display bicontinuous interpenetrating networks, reduced energy loss, and suppressed charge carrier recombination losses. Hence, an excellent PCE of 18.20% is achieved for the D18:BTP-eC9-4F:SM16 ternary devices, which is much higher than D18:BTP-eC9-4F-based binary ones and also one of the highest PCEs for the green-solvents-processed OSCs. Besides, this strategy also demonstrates a good universality for other binary systems and becomes an effective pathway for the development of green-solvent processable high-performance OSCs.

A novel and efficient strategy is developed for the annealing-free solution prepared SnO₂ electron transport layer for perovskite solar cells (PSCs). Through simple electrochemical regulation low defect concentration and optimized band alignment is acheived for PSC devices. A device power conversion efficiency (PCE) champion of 24.7% is reported with V _OC champion of up to 1.19 V, in addition to a large area device PCE of 21.3%.

Abstract

The electron transport layer (ETL) plays a crucial role for efficiency and stability of perovskite solar cells (PSCs). As a promising low-temperature ETL, tin oxide still requires complicated surface chemical decoration or heat-treatments to further passivate the defects and adjust band energy level to improve the optoelectronic performance of the device. Herein, a novel and efficient strategy is developed for the solution prepared annealing-free SnO₂ ETL for PSCs. Through simple electrochemical regulation, the elemental composition, valence ratio of Sn, concentration of oxygen vacancies, hydroxyl groups, and dopant ions are precisely modified with the optimized the energy band, reduce the defect density, and enhance high carrier transport for PSCs. Thus, an increase of power conversion efficiency (PCE) from 21.6% to 24.7% and a high V _OC of 1.19 V is obtained. The modified devices maintain 95% of the initial PCE after 2000 h of storage, and 80% of the initial PCE after 900 h of aging in an atmospheric environment at 75 °C and RH 20 ± 5%. Moreover, the perovskite solar module based on the as made SnO₂ achieve a high PCE of 21.3%.

A high-performance and stable perovskite solar cell is demonstrated by using a fluorinated indoloindole (IDIDF)-based linear-type hole transporting material. The perovskite solar cell using IDIDF2 achieves high performance in non-doped (23.16%) and doped conditions (24.24%), respectively. In addition, the corresponding devices show superior device stability under continuous thermal aging (85 °C) and humid atmosphere (85% relative humidity).

Abstract

The new concept of hole transporting materials (HTMs) has inspired researchers to develop high-performing and stable perovskite solar cells (PSCs). In particular, small molecular organic semiconductors have been extensively studied for HTM due to their high reproducibility and easy synthesis. In this work, a novel linear-type series of indoloindole (IDID)-based hole transporting materials comprising a fluorinated IDID core(IDIDF) and multiple thiophene rings is developed. The structure-property relationship in the IDIDF derivatives is investigated systematically by changing the alkyl position and length of the backbone. The intrinsic properties of the material are significantly different depending on the alkyl position of inner thiophene ring. The optimized material exhibits improved solubility, favorable molecular packing patterns, and superior hole mobility. The champion PSCs using the optimum molecule, IDIDF2, yield a power conversion efficiency of 23.16% in non-doped and 24.24% in doped conditions, which represent one of the highest performances in n-i-p planar device configuration. For the first time, the IDIDF2-based PSCs achieve outstanding thermal and moisture stabilities under thermal aging (85 °C) and relative humidity of 85%, respectively, for 1500 h.

A strategy for highly efficient and robust perovskite solar cells via a greenable slot-die process is reported. Locally supersaturated perovskite ink based on low-toxic dimethyl sulfoxide is prepared by rheological engineering with a small amount of 1,2-dichlorobenzene . The findings present a strategy for designing perovskite inks and a pathway toward the future commercialization of perovskite solar cells.

Abstract

Perovskite solar cells (PSCs), which debuted with a lot of attention based on high efficiency, are establishing as one of the most promising thin-film photovoltaic technologies. Currently, research for upscaling and commercialization through eco-friendly solvent and process systems is being attempted. This study introduces for the first time a rheological engineering-based locally supersaturated perovskite ink (LSPI) strategy for slot-die process-based PSC fabrication suitable for roll-to-roll continuous processes. Here, for the greenable slot-die process, a perovskite precursor ink composed of a low-toxic dimethyl sulfoxide (DMSO) single solvent is used and a small amount of 1,2-dichlorobenzene (DCB) is utilized as a modulator to control the rheological properties of the ink. The addition of DCB lowers the high surface tension of the DMSO-based perovskite precursor ink to suit the slot-die process, enabling uniform wet film formation, and produces locally supersaturated colloids, i.e., perovskite seeds, that help growth into dense and large grains by heterogeneous nucleation with low Gibbs-free energy. As a result, the LSPI enables slot-die coating-based PSCs with an efficiency of 20.61% (active areas of 0.1 cm²), which allow high efficiencies of 18.66% and 17.66% (active areas of 2.7 and 8.64 cm²) to be achieved in scale-up to minimodules, respectively.

The π-expansion of phenazine-fused core on AQx-18 affords a 2D-congjugated non-fullerene acceptor with favorable electronic and aggregation structures. AQx-18-based devices exhibit a PCE of 19.1%, which is among the highest value ever reported for organic solar cells (OSCs) with a high V _oc of 0.928 V. Such a 2D π-expansion strategy is promising for next-generation high-performance OSCs.

Abstract

The π-expansion of non-fullerene acceptors is a promising method for boosting the organic photovoltaic performance by allowing the fine-tuning of electronic structures and molecular packing. In this work, highly efficient organic solar cells (OSCs) are fabricated using a 2D π-expansion strategy to design new non-fullerene acceptors. Compared with the quinoxaline-fused cores of AQx-16, the π-expanded phenazine-fused cores of AQx-18 induce more ordered and compact packing between adjacent molecules, affording an optimized morphology with rational phase separation in the blend film. This facilitates efficient exciton dissociation and inhibited charge recombination. Consequently, a power conversion efficiency (PCE) of 18.2% with simultaneously increasing V _oc, J _sc, and fill factor is achieved in the AQx-18-based binary OSCs. Significantly, AQx-18-based ternary devices fabricated via a two-in-one alloy acceptor strategy exhibit a superior PCE of 19.1%, one of the highest values ever reported for OSCs, along with a high V _oc of 0.928 V. These results indicate the importance of the 2D π-expansion strategy for the delicate regulation of the electronic structures and crystalline behaviors of the non-fullerene acceptors to achieve superior photovoltaic performance, aimed at significantly promoting further development of OSCs.

Narrow-bandgap Sn-Pb perovskite films doped with SnO_x exhibit improved film morphology, crystallization, optical properties, and more interestingly, an upshifted Fermi level. Consequently, SnO_x-doped devices have considerably reduced defects and improved transport of major carriers, resulting in a maximum efficiency of 22.16% for Sn-Pb single-junction cells and a remarkable efficiency of 26.01% for two-terminal all-perovskite tandem cells.

Abstract

Narrow-bandgap (NBG) mixed tin/lead-based (Sn-Pb) perovskite solar cells (PSCs) have attracted extensive attention for use in tandem solar cells. However, they are still plagued by serious carrier recombination due to inferior film properties resulting from the alloying of Sn with Pb elements, which leads to p-type self-doping behaviors. This work reports an effective tin oxide (SnO_x) doping strategy to produce high-quality Sn-Pb perovskite films for utilization in efficient single-junction and tandem PSCs. SnO_x can be naturally oxidized from tin diiodide raw powders and successfully incorporated into Sn-Pb perovskite films. Consequently, Sn-Pb perovskite films doped with SnO_x exhibit dramatically improved morphology, crystallization, absorption, and more interestingly, upward-shifted Fermi levels. The resulting narrow-bandgap Sn-Pb PSCs with natural SnO_x doping have considerably reduced carrier recombination, therefore delivering a maximum power conversion efficiency (PCE) of 22.16% for single-junction cells and a remarkable PCE of 26.01% (with a steady-state efficiency of 25.33%) for two-terminal all-perovskite tandem cells. This work introduces a facile doping strategy for the manufacture of efficient single-junction narrow-bandgap PSCs and their tandem solar cells.

Multiple iodine-related defects in CsPbI_3−x Br _x perovskite solar cells (PSCs) were inhibited by the synergistic effects of halogen, coordination, and hydrogen bonds of 2,6-diaminopyridine (2,6-DAPy). This results in an excellent power-conversion efficiency of 21.8 % for the 2,6-DAPy-CsPbI_3−x Br _x PSCs, alongside significantly enhanced humidity stabilities of unencapsulated cells.

Abstract

Halide-related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long-term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (I_i) has a low formation energy similar to that of the iodine vacancy (V_I) and is also readily formed on the surface of all-inorganic perovskite, and it is regarded to function as an electron trap. We screen a specific 2,6-diaminopyridine (2,6-DAPy) passivator, which, with the aid of the combined effects from halogen-N_pyridine and coordination bonds, not only successfully eliminates the I_i and dissociative I₂ but also passivates the abundant V_I. Furthermore, the two symmetric neighboring -NH₂ groups interact with adjacent halides of the octahedral cluster by forming hydrogen bonds, which further promotes the adsorption of 2,6-DAPy molecules onto the perovskite surface. Such synergetic effects can significantly passivate harmful iodine-related defects and undercoordinated Pb²⁺, prolong carrier lifetimes and facilitate the interfacial hole transfer. Consequently, these merits enhance the power-conversion efficiency (PCE) from 19.6 % to 21.8 %, the highest value for this type of solar cells, just as importantly, the 2,6-DAPy-treated CsPbI_3−x Br _x films show better environmental stability.

Nature Materials, Published online: 01 June 2023; doi:10.1038/s41563-023-01561-w